SpringBoot Remove redundant configuration of ReactiveElasticsearchTemplate.setRefreshPolicy(RefreshPolicy.IMMEDIATE)

See #30096 for background.

We currently call ReactiveElasticsearchTemplate.setRefreshPolicy(RefreshPolicy.IMMEDIATE) which is redundant as RefreshPolicy.IMMEDIATE is the default. Should the default in Spring Data Elasticsearch change in the future, things will then get out of sync. We should remove the call to setRefreshPolicy so that we always use whatever the SD Elasticsearch default is.